The present invention relates to a surround to be attached to the edge of a diaphragm of a speaker system, and a manufacturing method thereof.
The present application claims priority from Japanese Application Nos. 2002-098131 and 2002-290640, the disclosure of which is incorporated herein by reference.
Surround is a speaker component fitted to an outer peripheral edge of a diaphragm for flexibly supporting the diaphragm on a speaker frame. It is for holding the diaphragm in place and should satisfy the following requirements: an ability (linearity) to move the periphery of the diaphragm linearly when a driving force is applied to the diaphragm, an ability to suppress lateral vibration of the diaphragm, and good air tightness so that sound waves reflected by the backside of the diaphragm are not released to the front side thereof. It is also important that no intrinsic resonance occurs in the surround itself when it vibrates by the actuation of the diaphragm for the sound amplification.
Shape and material of a speaker's surround are thus designed according to desired speaker performances in consideration of these requirements. Surrounds for cone diaphragms are most commonly formed in a rolled shape which protrudes to the outside of the diaphragm, and made of a molded rubber or press-formed urethane foam. There are two methods of forming a surround at the edge of a diaphragm: One is a method of bonding a separately prepared surround to the edge of a diaphragm, and the other is a method of integrally forming a surround and a diaphragm made using different materials with a mold-set (see Japanese Patent Laid-open Publication No. 2000-261885).
In a high-power, high-output speaker system such as a subwoofer speaker system, a malfunction or breakage sometimes occurs in the surround, resulting from the large vibration amplitude of the diaphragm and the high pressure inside the speaker enclosure.
This is because the conventional speaker's surround has a rigidity which is insufficient for the high-power, high-output speaker system. When a negative pressure increases inside the speaker enclosure, the rolled surround protruding outwards is sucked inwards. The surround shape is deformed because of this inward buckling, whereupon the surround can no longer exhibit its abilities to move the diaphragm linearly, to suppress lateral vibration of the diaphragm, and to prevent intrinsic resonance of the surround itself. The diaphragm then moves irregularly and intrinsic resonance occurs in the surround, resulting in distortion at low sound levels and noises.
If the surround is made of a urethane foam material, it may eventually break, because the material cannot withstand repeated vibration with a large amplitude in the high-power, high-output speaker system.
The rigidity of the speaker's surround could be increased simply by making the material thickness larger, but this will increase its weight and lower the speaker efficiency, and high sound pressure levels can not be achieved.